1. Field of the Invention
This invention relates to imaging of objects by laser radar and more particularly to imaging based on an array of semiconductor detectors.
2. Background Information
Laser techniques, such as LADAR (Laser Detection and Ranging) or “LIDAR” (Light Detection and Ranging), are used to image objects in three-dimensional image systems. Light, often from a laser source, is directed toward an object of interest. Reflected light from the object is then gathered and focused on one or more photodetectors.
LADAR and LIDAR systems are capable of determining the distance to an object, for example, by timing the travel time of light pulses sent round trip from a source to the object and back to a detector. However, adapting such systems to image remote objects challenges the sensitivity and speed of available devices.
In some laser imaging systems either the scanner or the receiver is scanned across the object, and multiple laser pulses are used to probe the contours of the object. An example of such an approach is shown in U.S. Pat. No. 6,734,849, issued to Dimsdale et al. on May 11, 2004.
Scanner-less approaches have been described as well. Marino, in U.S. Pat. No. 5,892,575 (1999), describes two categories of laser radar systems: scanning and scannerless. Scanning systems include a mechanical device for aiming a laser toward discrete points and for collecting light reflected from those points. Scannerless systems use an array of detectors to detect light reflected from a scene. A processor records the position of light detectors within the array that detected the reflected light and the corresponding travel time of the pulse of light to each of the detectors.
Scanning systems tend to be expensive. The mechanics of the scanner are complex. They also increase the weight of the system and reduce reliability. Scannerless systems, on the other hand, have difficulty building an accurate three-dimensional scene from a series of discrete images.
What is needed is a system and method for imaging that addresses the above shortcomings, and other shortcomings that will become apparent in reading the following description.